1. Field of the Invention
The present invention relates to a technique which generates an image within an object, on the basis of a projection data obtained by irradiating the object with X-rays. More particularly, it relates to an X-ray CT apparatus which quantifies a fat content in a predetermined region, from such an image.
2. Description of the Related Art
The progress of a X-ray CT (Computed Tomography) apparatuses in recent years is remarkable. In compliance with the eager desire of medical treatment sites to radiograph a human body or the like at a higher precision (resolution) and in a wider range, a multislice X-ray CT apparatus has been developed and has come into considerably wide use. The multislice X-ray CT apparatus is configured including an X-ray source which irradiates an object with cone beam X-rays having a spread width in a slice direction (a lengthwise direction of a table-top), and a two-dimensional detector in which a plurality of detection element rows are arrayed in a slice direction, whereby helical scan can be performed. Thus, as compared with a single-slice X-ray CT apparatus, the multislice X-ray CT apparatus can obtain volume data over a wider range within an object, at a higher precision and in a shorter time.
With such an X-ray CT apparatus in the prior art, in a case, for example, where the liver part of a patient has been radiographed, the advanced degree of fatty liver is sometimes judged from the visual impression of a diagnostician for an obtained image, a CT number measurement based on a region of interest (ROI), or the like. The judgment of the advanced degree of the fatty liver, however, depends greatly on the subjectivity of the diagnostician.
Besides, measured the CT number tend to involve a size-dependency in accordance with the discrepancy of the physique of the patient. Therefore, it cannot be always said an appropriate diagnosis to judge the advanced degree of the fatty liver on the basis of the CT number measured without taking the physique of the patient into consideration.